It is known to construct such valves for recovering a certain thrust generated because the pressure Pi inside the aircraft is higher than the pressure Pa outside the aircraft. Conventional flap valves of this type comprise one or several flaps. The position of these valve flaps or gates relative to a valve opening is controllable by a drive mechanism inside the aircraft. The drive is normally controlled in closed loop fashion by a feedback control. The flap normally stays open or the flaps normally stay open as long as there is a positive pressure difference between the air pressure inside the aircraft and the atmospheric pressure outside the aircraft. Depending on the position of the flaps, particularly if the flaps are closed, the internal pressure inside the aircraft may be adjusted to provide a negative differential pressure. The valve flaps generally have plane surfaces or edges for forming an air discharge gap and outwardly facing surfaces adapted to the aircraft contour.
German Patent Publication DE 197 13 125 A1 (Steinert et al.) discloses a stage valve that has a first smaller stage (20) and a second larger stage (30). The first valve stage (20) and the second valve stage (30) are coupled with a drive gear (40) in such a way that the first smaller valve stage can be operated separately from the second larger valve stage. In one conventional embodiment the smaller valve stage has a centrally journaled flap mounted within an opening of a larger flap. In the other conventional embodiment a larger flap and a smaller flap are each centrally journaled. Thrust recovery is accomplished in each conventional version, particularly during cruising flight when the internal cabin pressure is substantially larger than the external atmospheric pressure at cruising altitudes. In the other conventional embodiment one flap (70) has a bulging broadened end (73) for diverting the air stream onto a guide plate (76). The valve stages are supposed to have aerodynamically beneficial characteristics. However, a nozzle for the air discharge is not formed. Just air discharge channels are formed.
U.S. Pat. No. 3,426,984 (Emmons) discloses an aircraft pressurization outflow valve with two flaps each hinged at its end opposite the flap end edges (40, 42) that form an air outflow gap. These flap end edges (40, 42) form a convergent or convergent-divergent nozzle for effectively recovering thrust from the air discharging out of the cabin into the airstream around the aircraft outer body skin.
Further conventional air discharge valves similar to the above described valves are illustrated in present FIGS. 1, 2 and 3. FIG. 1 shows an air discharge valve installed in the airbus model “320/A340”. FIG. 2 shows an air discharge valve installed in the aircraft model “Boeing 777”. FIG. 3 shows an air discharge valve installed in the aircraft model “Boeing 737”. These conventional valves function as pressure control valves operating in response to a closed loop control signal.
Conventional valves as described above leave room for improvement particularly with regard to noise reduction, particularly in the below critical pressure range. Conventional valves also leave room for improvement with regard to making the thrust recovery more efficient, particularly for a positive pressure difference ΔP when the internal pressure Pi is larger than the external pressure Pa.